English

When an Equivalence Relation with All Borel Classes will be Borel Somewhere?

Logic 2016-08-18 v1

Abstract

In ZFC\mathsf{ZFC}, if there is a measurable cardinal with infinitely many Woodin cardinals below it, then for every equivalence relation EL(R)E \in L(\mathbb{R}) on R\mathbb{R} with all Δ11\mathbf{\Delta}_1^1 classes and every σ\sigma-ideal II on R\mathbb{R} so that the associated forcing PI\mathbb{P}_I of I+I^+ Δ11\mathbf{\Delta}_1^1 subsets is proper, there exists some I+I^+ Δ11\mathbf{\Delta}_1^1 set CC so that ECE \upharpoonright C is a Δ11\mathbf{\Delta}_1^1 equivalence relation. In ZF+DC+ADR+V=L(P(R))\mathsf{ZF} + \mathsf{DC} + \mathsf{AD}_\mathbb{R} + V = L(\mathscr{P}(\mathbb{R})), for every equivalence relation EE on R\mathbb{R} with all Δ11\mathbf{\Delta}_1^1 classes and every σ\sigma-ideal II on R\mathbb{R} so that the associated forcing PI\mathbb{P}_I is proper, there is some I+I^+ Δ11\mathbf{\Delta}_1^1 set CC so that ECE \upharpoonright C is a Δ11\mathbf{\Delta}_1^1 equivalence relation.

Keywords

Cite

@article{arxiv.1608.04913,
  title  = {When an Equivalence Relation with All Borel Classes will be Borel Somewhere?},
  author = {William Chan and Menachem Magidor},
  journal= {arXiv preprint arXiv:1608.04913},
  year   = {2016}
}
R2 v1 2026-06-22T15:22:04.886Z